Manufacture of boron trifluoride



Feb. 1s, 1947.

DE WALT S. YOUNG ETAL MANUFACTURE 0F B'ORONV TRIFLUORID Filed June 1e, 1944 .pAA//v IN VEN TOR.

, *V/Mgg@ ATTQRNEY Patented Feb. 18, 1947 i V t 2,416,133l 'ci i MANUFACTURE oF BORON TRIFLUORIDE De Walt- Secrist Young, Kingsport, Tenn., and I J ohnH. Pearson, Manhasset, N. Y., assignors to i IGeneral Chemicall Company, New York, N. Y., a

. :corporation of New York ApplicationJun'e 16, 1944, Serial N0, 540,612

This invention relates to manufacture of boron triuoride; 1

f Fluosulfonic acid (HSOaF) and boric acid itself (H3303) or any of its dehydrated forms such as metabo'ric acid (H1302), pyroboric acid (HzBflOr) and'bori'c anhydride (B203), may be reacted to' form'BFa gas andliquid sulfuric acid as a byproduct. This invention aims to provide a process formaking BF3 gas continuously and preferably under substantial superatmospheric pressure. Other-major objects are to provide procedure by the practice of which it is possible to obtain high BFs gas yieldby elfectingrapid reaction vof reactantsand minimizingsolubility of BFa in byproduct sulfuric acid notwithstanding permissive relatively high pressures at which the process may be carried out.` The preferred boron compound employed in carrying out the improved process is commercial solid boric acid (HaBOs) and the herein presented description of the invention is given mostly in connection with use of this material. Y

` The invention, its objects and advantages may be more'fully understood fromv the following description taken in connection with the accompanying drawing showing apparatus, partly in section and partlykdiagrammatic, lin which apre-y ferred embodiment ofthe process may be carried l *Referring tol the drawingfl indicates `a vertically elongated reactor designed to withstand internal pressures of say Z50-350 -lbs.per square inch gauge; The reactor is made preferably of iron which term, in this specicationand appended claims,` is intended to'include commonly known grades ofrsteel. Near the upper end, the reactor is 'provided with a BFa gas outlet II-,Aand at the bottom withan outlet I2 thru which" sulfuric acid by-product of =the reaction may be discharged. lLiquid fluo'sulfonic vacid and sulfuric acid liquor containing boric-acid'in solution are pumped into the Ytop of the reactor thru inlets at l5 and I6 respectively. lA safety valve `I1fisoperatively associatedwith the gas space in the top ofthe reactor. g' i i On one side of the reactor isa cylindrical extension i20, offsubstantial diameter, havinga closure platef2l. VThe latter acts-as a'supportfor a float 24 thearm 25 of `which is` suitably fulcrumed as'at 21. `The outerrend 28 rof'arm 25 controls a valve 3B which in turn 'regulates the quantity of liquid discharged.from'the-reactor thru pipes 32` and l33. Liquor passing valve 30 is conducted byv pipe 35andgvalve-controlled connections 31 and 33 into solution make-up 'tanks 40 and 4l "or' .to

7 Claims. (o1. 23-205) 2 c Y an outlet 43 fromfwhichexcess by-product sulfurie acid may be discharged from the' system.. `While float 24 may be located conveniently at about the mid-point of the vertical height of the, reactor, any other position is suitable so long .asy extension 2i)v andthe float arevplaced so as to facilitate maintenance'in the bottom of the reactor of a sulfuric acid liquid pool of substantial` depth. Ordinarily such pool should ll the reactor to at least a third of its capacity. That portion of the.Y lower section of the'reactor occupied by the liquidv pool is preferably entirely surrounded Vby a steam jacket or coil 46, the inlet 41 of which'iscon nected'to a source of steam under pressure.V l n Projecting downwardly from the reactor cover 1 49 are baille plates 50 and 5| usuallyarranged as shown on the drawing. lThese plates maybe ref, placed by any suitable mechanical means which'j promote good mixing of incoming uosulfonic acid and sulfuric acid liquor containing boricacidin-SOlutiOn.`V For example, a'grid support and loosey tile packing may be employed in the top of the tower. Alternatively, fluosulfonic acid and su1` furic acid liquor containing boric acid in solution may be charged into the reactor at a common in j` let point, in which case good mixing of reactants would be obtained initiallyand no mechanical' mixing devices in the top of the reactor would bey necessary. Thus the space between the surface 55V ofthe liquid poo156 and the top of the-reactor provides an unobstructed reaction zoneV 51, this term being used in the sense that, whether or not the upper end of the reactor contains bailles or Y' and that in reaction zone 51 there is nothing in the nature of an unbroken body of liquid as existsy in the bottom of the reactor. l

The iiuosulfonic acid used may be'commercial' uosulfonic acid ordinarily running in excess 'of 95% HSOaF and possibly containing some small' amounts of S03 in solution.V Also, redistilled fluo-r sulfonic acid containing substantially no SO?` may"- be employed. In starting up the process, one sol lution tank e. g. tank 40'is partly filled with com--A mercial sulfuric acid" of 1 preferably "99-100-70' strength. Solid boricacid is run into tank 40thru rdinarily sulfuric acid liquors having boric acid concentrations of -25% are employed. When any of the dehydrated forms of HxBOa are employed in place of or in conjunction With HsBOs,

the quantities of other forms used are such as to provide boron concentrations',equivalent to the boron concentrations 'when H3B03 itself is 'uti-A lized.'

Steam is admitted to the 'jacket 4S, and the reactor is brought up t temperature of about 100 C. Cold water 4is run into -and thru the cooling chamber, not shown,.of.gas cooler 52.

Valves 64 and 65 near the bottom "ofthe r'reactor are closed. Y i

Pumps 61 and 68 are started up, and sulfuric acid liquor containing boric acid ,in `solution, and uosulfonic acid are fed into the top V'of 'the re'- actor thru pipes 69 and 1li respectively. ',Boric acidV and luosulfonic acid react in accordance Ar tor. Theforegoingprocedureiis'followedun- "e liquorinthe lreactor Vrises to approximately tine ,level 'sis' and une; tire 'system is ,purged Q'f air. after, fthe .valve line 16 isz closed, and red valve T8 'is `adjusted Ito create `in 15. and the reactor VWhatever .gas .presed for operation. v `Y 4 v t rlevel inthe reactor rises sucientlylto contact vfloat 2l, valve 16'5 opened Wide and then the loatcontrolsvalve 30 which, .in conjun on rWith'ithe float, .is adjusted Aso-as torrnaintalinlthe, surfaceof the liquid poo-l 5'6`at apprcxif Inatelylconstant level. l In vthe succeeding normal operation ofthe process, sulfuric .acid liquoris OCedby ,the pressure existing Vvin the reactor thi P'De 13.3, Valve 30,. and pipo 135 either into malgefup v.tanks ll and `lll `Yor to the pointof discharge @A3-Q In. banks 140 and l. sulfuric. acid liquors.. 'Containing borioaoid in solution; of the type. pre ouslydescribed are continuously made umpyas ,beolje @XC-@llt that ley-product sulfuric acid is .u'sedvin place 4ofi-fresh commercial acid.

Weile tboproooss. .0i this invention may be used.

to, fcrrn Bls @gas under any appreciable super.- aimosehorioprossuie as -low evs-Sayy 3-5 lbS- sauge, a ,/IHJaJ'QrVK feature .lof the present improvements lies-in,continuousproduction of Vllifa' gas Vat relatively high pressures, te. g. '7G-250 glbs. 'gaugef An important use of BB3 is as acata-lyst in various ohemical'prooosses opor-ated vunder pressures of the `order of 10Q- 209 lbs. This invention :proviolosa process which.,forexamp1e, may be carriedipout'by 'a user of BFS` toproduce BFa` gasfat an elevated lpressurethe same as or above the pressure existing in the process in Which'the BB3 is to be employed. Thus BFs gas made underl pressure inaccordance with the `process of this invention may 'be fed directly to another pressure processusing BFaras a reactantzor catalyst. Fur- Y ther,- forfgeneral sales purpOSesBFa gasis-stored and 'transported in cylinders undervery high pressuigesof '1800.110 2000 lbs. gauge. Formation of `Blis-atfthe high pressures` attainable by the.

4 of the HgBOa-HSOsF reaction as a compression agent, and arise from the discovery of certain koperating conditions which o-iset the materially reduced yields characterizing processes in which a sought-for product is a gas.

In developing Ila continuous-process ofv-ethis na-` ture, some ofr the principal. dperaiting.problems encountered comprised (a) kmode of feed of boric Y facid (commercially a'solid material) to the reaction zone, (b) provision of a majorreaction zone of such nature as to a'ord intimate contact of reactants while in their most concentrated condition, ready separability of BFs gas and byproduct sulfuricacid, and substantially immediate "removal Voflicluidffrorn the zone of major reaction, vto therebymake possible a high rate of reacition and cu't'down opportunity for sulfuric acid to 4absorber dissolve BFS, (c) reduction of solubility of BF3 gas in thesulfuric acid discharged from the reactor, (d) ,selection of materials ,out-.of which the reactor and associated vecluiifirnerit may be made, and -(e) r minimization vof SO2 content of BFsga'sproduced. I A. d

In practice of the process, .particularly when vWorking at rrelatively loW pressures of .less than about 20 lbs. gaugait is .possibleftofeed in solid form into the reactor. vI-IovveverVsuch procedure even at relatively low pressures Vg'ifv'es rise .to difficulties, lin regard to proper proportioning .of the amounts Aof..reactantssupplied'to the reaction zone and to securing satisfactory dispersion and intimateco-ntact .of'liquid'luosulr ionic acid and `solid H3303. .Accordingily., `ina-al1 modifications of the process it v.is -preferired to supply lboric `acid to .the reaction Zone v-vvhilejin solution in sulfuric acid, since "this procedure facilitates :introduction of boricacid vagainst any pressure which Amay be prevailing :ein the reaction zone, and permits `accurate 4reactant .proportioning whichis an importantvrfactor ofsuccessful operation. Moreover, utilization of sulfuric .acid as a boric acid carrier avoids -Iintroductionainto the reaction zone of any ingredient or-impurity other than -sulfuric acid, .a material necessarily formed as a resultof theIfIaBOa-HSOsF reaction itself. ndditionally, We `Alnd that sulfuric acid liquors containing the preferred r20-25 %"by weight `concentration of HsBOa are of satisfactory viscosityvandrvare readily amenable toY handlingiin afproportioningvpump. Also, -fintroduction of boricacidin liquid vcarrier affordsxgood 'dispersion o fboricacid and adequate mixing with 'fluosulfnic acid. Y v v t -We have discovered that .intimate "contactwof reactants While linthe.mostconcentrated. condi tion, ready separability of BFs gasand by-tproduct sulfuric facid, and substantially VAimmediate "ree moval iofjliquid' l'from Vthe yarea of -major reaction may be had by'introducingtheV 'il'uosulfonicv acid and thesulfuriciacid liquor containing boric acid in solution kinto van unobstructed lreaction zone. In Vthe embodiment `under consideration, tem-` p'eraturesimay-beas low as 50-'80 lC.,'particularly in the top of reaction zone 57. Notwithstanding suchlow reaction temperatures, Whichzcontribute to corrosion reduction,y four linvestigations ssho'w that on introduction fof -the y-iuos'ulfonic acid and the sulfuric 'acid n'liquor zcontaining'boric acid fin solution Ainto an Aunobstructed zone, the HSOsF and Ha'BOa reaction i's `substanti'all'yaash'fopsulfuric.vx acid, and vfsubstanti'ally fim'mediate fire-i moval of'liqud from the zone of major reaction Y'serieuse are predominating features with respect to promoting a high rate of reaction and minimization of the opportunity for sulfuric acid to dissolve BFa. These ends maybe accomplished by utilization of an unobstructed reaction zone.

Investigations carried out during development of the invention show that BFa gas is markedly less soluble in sulfuric acid containing HSOaF than in sulfuric acid containing HaBOs. For example, at temperature of 30 C. and atmospheric pressure, sulfuric acid containing 1.9% HaBOs (by Weight) contained 5.1% BFs, while on the other hand sulfuric acid containing 2.2% I-ISO3F contained only 1.9% BFa. At temperature of 100 C. and atmospheric pressure, sulfuric acid containing 4.3% H3BO3 contained 6.1% BFs, while sulfuric acid containing as much as 8% HSOsF contained only 0.9% BFa. At temperature of 100 C. and pressure of 200 lbs. gauge, sulfuric acid containing 3.9% -HaBOa contained 9.7% BFs, and sulfuric acid containing as much as 12.5% HSOsF contained only 1.3% BFa.

It has also been found that as the H3BO3 content of a sulfuric acid liquor increases, the solubility of BFa also increases. Thus, at temperature of 30 C. and atmospheric pressure, sulfuric acid containing 1.9% HaBOa contained 5.1% BFa, and sulfuric acid liquor containing 4.6% HaBOs contained 9.4% BFs. and atmospheric pressure, sulfuric acid liquor containing 1.9% HsBOs contained 2.9% BFs, while at the same temperature and pressure conditions when the I-IsBOs content was 4.4%, soluble BFs At temperature of '100 C.

increased to 6.1%. In the case of sulfuric acid f containing iluosulfonic acid, as HSOaF content increases, solubility of BF?. decreases. At temperature of C. and atmospheric pressure, a sulfuric acid containing 2.2% HSOsF contained 1.9% 'BFL but When the HSOaF content was increased to as much as 13.8%, solubility of BFa dropped to 1.5%. At temperature of 100 C. and atmospheric pressure, sulfuric acid liquor containing 8% HSOaF, contained only 0.9% BFa, and at temperature of 100 C. and pressure of 200 lbs. gauge, sulfuric acid liquor containing 12.5% HSOaF contained only 1.3% BFs.

Further, it has been found that solubility of BF; in sulfuric acid containing some HSOsF is appreciably less than the solubility of BF: in straight sulfuric acid, i. e. sulfuricv acid .containing no HsBOa or HSOsF. At temperature of 30 C. and atmospheric pressure, straight sulfuric acid contained 2.7% dissolved BF3, while sulfuric acid containing 2.2% HSOaF, contained 1.9% BF3. pressure, straight sulfuric acid contained 1.1% dissolved BFs, while sulfuric acid containing as much as 8% HSOaF contained only 0.9% BFa. At temperature of 100 C. and pressure of-200 lbs. gauge, straight sulfuric acid dissolved 3.1% BFa, but sulfuric acid liquor containing as much as 12.5% HSOaF contained only 1.3% BFa.

Accordingly, in practice of the present invention the quantities of HsBOa and HSO3F fed to the reaction zone are such that theby-product sulfuric acid contains no H3BO3. While reasonably good results with respect to low solubility of BFa in by-product sulfuric acid may be obtained by feeding to the reaction zone HaBOa and at least a stoichiometrically reacting proportion of fluosulfonic acid, it is preferred tosupply the reaction zone with H5031 in quantity in excess of that reacting stoichiometrically with HaBOa, so as to assure the presence, of some HSOsF in ,the ley-product sulfuric acidin thebottomof the At temperature of 100 C. and atmospheric i reactor. In the usualpractce of the preferred embodiments, proportioning pumpsl and 68 are adjusted so as to feed to reaction zone 51 nuosulfonic acid and boric acid in an HSOaFzI-IsBO: weight ratio of not less than 5:1. v

Another factor 0f importance in supplying heat to the major' reaction zone, effecting rapidity of reaction therein, and in reducing loss of dissolved BFsin the by-product sulfuric acid-discharged from the process is the temperature at which the sulfuric acid pool in the bottom of thfe reactor is held. Such temperature should be not less than C.` ,Some heat is developed during the HaBOa-HSOaF reaction, and to keep the sulfuric acid in the bottom of the reactor at proper temperature, only a relatively small amount of extraneous heat in the medium of steam supplied to jacket 46 is necessary. As previously noted, temperatures in the unobstructed reaction zone are materially less, usually of the order .of y'l0-80 C., and in the top of such reaction zone, at approximately the point of introduction Aof 4fluosulfonic acid and sulfuric acid liquor containing boric acid in solution, temperature may be locally as `low as 50 C. in the area where most ofthe BFS gas is formed. In general practice of the process, pool temperatures in excess of say 12S-135 C. afford no worthwhile operating advantage.

It has been found that the process maybe most satisfactorily and economically carried out in an iron or steel reactor, other accessory equipment being made of the same material. In most processes in which BFS gas is used as a reactant or catalyst, the presence of SO2 in the gas is objectionable; In this connection it has been demonstrated that, when using iron or steel apparatus, in order to hold the SO2 content of the BFa product gas to a desirable minimum, e. g. not more than 1%, and

preferably substantially less, temperature of the pool of by-product sulfuric acid in the bottom of the reactor should be held not in excess of 105 C. Thus, temperature of pool 56 may be kept at -105 C., and the preferred working temperatures are 95-100 C. Maintenance of the desired pool temperatures may be had by adjustment ofl the pressure of the steam supplied to jacket 46.

Preferably, the heating jacket or coils surround substantially the entire circumference of pool Ifili to facilitate the relatively close temperature control indicated. In situations in which iron or steel apparatus is employed, and relatively high SO2 content in the product gas is permissible, pool Vyield and low solubility of BF: in the sulfuricacid.

It is preferred to control rate of discharge of liquid ,so as to hold each increment of liquid inthe reactor for not less than four minutes. In usual practice of the preferred embodiments described, this result may be obtained by adjusting rate of liquor discharge so that the volume of liquid withdrawn per unit of time does not exceed, and is preferably a little less than, the volume of liquid charged into the reactor.

Product `gas leaving the reactor passes upwardly thru cooler B2 in which the gas stream is cooled down to temperature of about 40 C. in order to condense out any.. sulfuric acid vapor and Catch form BFa gas and by-product sulfuric acid, the steps comprising continuously maintaining in the bottom of a closed reactor a liquid pool comprising by-product sulfuric acid held at temperature of 85-135 C., continuously introducingv fluosulionic acid and boric acid in HSOaFzI-ISBO?, Weight ratio of not less than 5:1 into a reaction zone above said pool, rapidly mixing the boric and fluosulfonic acids in said reaction zone so that BFa gas and liquid lay-product sulfuric acid are rapidly formed, continuously discharging BFS gas from saidreaction zone, collecting liquid byproduct sulfuric acid in said pool, and continuously discharging liquid from said pool at a rate such as to retain each increment of liquid Within the reactor for not less than four minutes.

'7. In the manufacture of boron trifluoride by reaction of boric acid and iiuosulfonic acid to form BFs gas and by-product sulfuric acid, the steps comprising continuously maintaining in the bottom of a closed reactor a liquid pool comprising by-product sulfuric acid, continuously intro- 10 ducing boric acid and at least a stoichiometrically reacting proportion of fluosulfonc acid into a reaction Zone above said pool, rapidly mixing the boric and luosulfonic acids in said reactionzone so that BFa gas and liquid by-product sulfuric acid are rapidly formed, continuously discharging BFs gas from said reaction zone, collecting REFERENCES CITED The following references are oi record in the le of this patent:

UNITED STATES PATENTS Name Date Hardtmann et al. Feb. 21, 1933 Number 

